1. Field of the Invention
The present invention generally relates to a liquid crystal displaying device and a liquid crystal displaying method. More specifically, the present invention relates to a liquid crystal displaying device and a liquid crystal displaying method which can effectively reduce power consumption and realize an optimum image quality.
2. Description of the Related Art
Techniques of high definition and high image quality in liquid crystal displaying devices or the like are rapidly developing along with a rapid increment of demands for the liquid crystal displaying devices or the like. Light sources of backlights employed in displaying on the liquid crystal displaying devices or the like are changing from Cold Cathode Fluorescent Lamps (CCFL) to Light Emitting Diodes (LED) and may be replaced within several years because the Cold Cathode Fluorescent Lamps (CCFL) have ecological problems such as a use of mercury and consumption power, and problems of image qualities such as contrast and color reproduction.
The LED backlights are employed in various technical fields such as portable phones, notebook computers, and small-sized monitors. Companies are planning to employ the LED backlights for middle to large-sized television sets and displays in future.
A schematic configuration of an example liquid crystal displaying device is described in reference to FIGS. 1A and 1B. FIGS. 1A and 1B illustrate the schematic configuration of the example liquid crystal displaying device. FIG. 1A illustrates an example liquid crystal displaying device using an example CCFL backlight. FIG. 1B illustrates an example liquid crystal displaying device using an example LED backlight.
The liquid crystal displaying device 10-1 illustrated in FIG. 1A includes a signal processing unit 11, a picture quality adjusting unit 12, a liquid crystal panel 13 as a liquid crystal displaying unit, a power source unit 14, and a CCFL back light unit 15. The liquid crystal displaying device 10-2 illustrated in FIG. 1B includes a signal processing unit 11, a picture quality adjusting unit 12, a liquid crystal panel 13, and a LED driver 16 and a LED backlight unit 17.
The liquid crystal displaying device 10-1 illustrated in FIG. 1A is provided to control brightness of a light source of the backlight. The image quality may be mainly improved using a single control system for a signal system. Specifically, when the liquid crystal displaying device 10-1 receives an image signal transmitted from, for example, a provider such as a broadcast station, the signal processing unit 11 carries out signal processing to enable an image contained in the image signal to be displayed on the liquid crystal panel 13.
The picture quality adjusting unit 12 adjusts the liquid crystal displaying device 10-2 to improve the image quality acquired by the signal processing unit 11 using predetermined conditions such as brightness, contrast, black balance and white balance.
The power source unit 14 supplies a predetermined amount of the power to the CCFL back light unit 15. In the CCFL backlight unit 15, lights emitted from the cathode tube as the light source repeatedly reflect on end surfaces of a light guide plate. Thus, the backlight is adjusted to be evenly luminous on the entire surface of the CCFL backlight unit 15.
The liquid crystal displaying device 10-1 makes visible an image signal included in an input signal by irradiating the surface of the liquid crystal panel 13 with the back light generated by the CCFL backlight unit 15.
The liquid crystal displaying device 10-2 illustrated in FIG. 1B is a LED backlight system provided to control the brightness of the backlight light source. In the liquid crystal displaying device 10-2 illustrated in FIG. 1B, the signal processing unit 11, the picture quality adjusting unit 12, and the liquid crystal panel 13 have functions substantially similar to the above liquid crystal displaying device 10-1. Therefore, descriptions of these same portions are omitted.
In a case where the backlight using LEDs is provided, groups of LEDs having colors of red (R), green (G) and blue(B) are arranged at predetermined positions, and the liquid crystal panel 13 is irradiated with the backlight generated by the groups of LEDs to thereby make visible the image signal.
Specifically, the picture quality adjusting unit 12 outputs information of the image signal to be made visible on the liquid crystal panel 13 to the LED driver 16. The LED driver causes the LEDs to emit light from a part of the LEDs at corresponding positions of the liquid crystal panel 13 on which the image signal is applied. Thus, the backlight of the liquid crystal panel 13 is realized.
For example, there is proposed a liquid crystal displaying device which improves an image quality of movies using a LED backlight (for example, Patent Document 1).
However, the above described CCFL backlight system tries to improve the image quality only with the single backlight source. Therefore, when the image signal does not conform to light distribution of the backlight, a blackout, a whiteout or the like may occur. In this case, there is a problem that an anticipated improvement is not obtainable. Further, the consumption power of the CCFL backlight system is larger than that of the LED backlight system.
Further, there is a regional brightness controlling technique (local dimming) using a top type backlight which is controlled relative to plural portions of a divided display screen in the above LED backlight system. In this local dimming, a change of the brightness in the vicinity of the divided boundary and the components of the image signal may overlap with a time interval. In this case, an unnatural display occurs and the image quality is degraded.
Patent Document 1: Japanese Laid-Open Patent Application No. 2008-15430